A distributor head of a distribution agricultural device is used for even distribution of seeds, fertilizing aggregate or other granulated material. It comprises a main inlet from a hopper of distributed material, which is usually fed to the distributor head by an air flow. The main exit is then divided by the internal mechanism of the distributor head into larger number of side outlets, which are arranged along the outer circumferential part of the distributor head. These outlets then distribute the granulated material to the individual exits evenly arranged on row units of the distribution agricultural device. As a result, even distribution of e.g. seeds on the area of processed soil is ensured.
When the field is of irregular shape or when adjusting tracks for different passages of sprinklers, it is necessary to selectively switch off some exits to avoid unnecessary waste of the distributed material on area not intended for growing crops. This selective switch-off is usually performed by mechanism which covers certain exits, so that the required extent is achieved.
Solution to this issue is presented, for example, in a patent document EP2269434 to Lemken company. A number of openings, which are used as side exits, are arranged along the circumferential part of the head at regular intervals. A mechanism for closing the individual exits is located in the inner part of the distributor. This mechanism consists of two, alternatively three, hoops. The first hoop has a number of openings arranged along its circumference, which correspond to the openings on the outer circumferential part of the head in terms of their position and number. Therefore, when using the first hoop, no openings are covered and seeds are distributed across the whole area. The second hoop has a number of openings arranged along its circumference, wherein the number of openings is lower than the number of openings of the first hoop, however, their positions correspond to some of the openings on the outer circumferential part of the head. As a result of using the second hoop, some openings are covered, which leads to changes in the area on which the seeds are sowed or fertilizer is distributed. A potential third hoop then ensures processing of another area. For example, with the second hoop, the left half of the distribution agricultural device is used, and the right one is used when using the third hoop. The disadvantage of this embodiment is the necessity to use at least two hoops, preferably three. These hoops move vertically within the distributor head. In practice, it often happens that the granulated material (seeds, fertilizer, etc.) gets into grooves, in which the individual hoops move. This causes the hoop movement to jam and it is necessary to disassemble and clean the distributor head, in order to ensure a fluent movement of the hoops.
Another solution to this issue is presented in a lapsed patent EP1478221 to Vaderstad company. Here, along the circumference of the outer part of the head, exit pairs are spaced in regular intervals. A closing device, which comprises a number of flaps, is located inside the inner part of the head. Depending on the position of the closing device, the flaps either cover none of the exits or half of the exits, thereby changing the extent of the area on which the granulated material is distributed. Because of the gaps between the individual exit pairs, the circumference of the distributor head is bigger than without gaps. This results in a need for a bigger head construction, i.e. poor folding of the whole structure of the distribution agricultural device and higher weight.